The Mechanism Research Of Synchronous Magnetic Field Control On Short-circuiting CO₂Welding

CO2welding method has been used widely because of the advantage of low cost andhigh efficiency. We will study the impact of external longitudinal magnetic fields on weldingprocess. Researching droplet force situation in initial and end stage of short circuit and arcingstage. The spatter and the weld will be changed because of the change of droplet transitionfrequency and strained condition, all these are caused by gravity, plasma jet force,electromagnetic contraction force, surface tension etc. Synchronous magnetic field controlCO2welding method has been developed based on above theory. The experiment content asbelow:（1） Doing CO2welding experiments with and without external longitudinal magneticfields. The base metal is Q235, and to study the droplet transition, spatter and weld formationwithin external longitudinal magnetic fields.（2） collecting the high speed photographypictures with and without longitudinal magnetic fields. The results as below:（1）the averagespatter will grow up at first and then get down gradually with the increasing of magnetic fieldsfrequency in a certain exciting current; the average spatter will get down first and then growup gradually with the increasing of exciting current in a certain magnetic fields frequency. Thebest welding parameter is2A of exciting current and60Hz of magnetic fields frequency, thearc expand obviously and rotating steadily, getting a high droplet transition frequency, and geta better weld formation. The biggest drop of spatter is4.99%within magnetic field control andthe decrease of weld reinforcement is0.61mm.（2） The arc and droplet in arcing phase willbe expanding in a horizontal direction within external magnetic fields, and the degree ofexpansion will be deepen with the increasing of magnetic field strength， and the arc will bebell shape from taper. In the process of short circuit, metal liquid bridge receivedelectromagnetic compression force within magnetic fields, and it s contribute to improvedroplet transition frequency and decrease short circuit time.We can get some results according to the force analysis of arc and droplet.（1） The balldroplet in arcing phase will received vertical downward force to promote short circuittransition process between droplet and molten in the magnetic fields and decrease droplettransition time, so the droplet transition frequency has been improved.（2） In the initial stageof short circuit phase, the contact radius and surface tension increased, and all these promoted the lateral spreading of droplet and weld formation, the spatter has been decreased too.（3）Inthe end stage of short circuit transition, electromagnetic compression force promote the breakof liquid bridge, and in this way to decrease short circuit time and improve droplet transitionfrequency and weld formation. Because of the shorten of short circuit time, the gatheredenergy in liquid bridge decrease accordingly, and then to decrease spatter caused by electricalexplosion.